I am working on an experiment that pairs one of 16 audio files with one of 96 visual files. I would like all 16 audio files to be presented once per trial, in a random order. I would like them each to be paired with a random visual file. However, when I pair the two lists, it presents 96 events, when I only want 16. How do I set my experiment so that the audio files are the limiting factor, and only a subset of 16 random visual files are presented per trial? Also, how do I ensure that each audio file is being presented once and only once over the 16 events in the trial?